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| United States Patent |
5,158,610
|
|
Bittner
|
October 27, 1992
|
Anticorrosive pigments on the basis of tertiary alkaline-earth aluminum
phosphates and a process for the production thereof
Abstract
The present invention provides anticorrosive pigments on the basis of
tertiary alkaline-earth aluminum phosphates, particularly those where the
numerical atomic ratio x:y:z of formula AE.sub.x Al.sub.y (PO.sub.4).sub.z
of alkaline earth to aluminum to phosphorus or phosphate is 50-70% to
5-30% to 20-50%. It also provides a process for their production in which
an alkaline-earth compound and aluminum compound sufficiently soluble with
phosphoric acid are reacted with phosphoric acid, the precipitated pigment
is filtered off as usual and dried, optionally calcined and optionally
ground.
| Inventors:
|
Bittner; Annegret (Lagelsheim, DE)
|
| Assignee:
|
Dr. Hans Heubach GmbH & Co. KG (DE)
|
| Appl. No.:
|
582339 |
| Filed:
|
September 14, 1990 |
Foreign Application Priority Data
| Current U.S. Class: |
106/462; 106/14.12; 106/14.13; 106/14.14; 106/14.21; 423/305; 423/503; 423/629; 423/DIG.8 |
| Intern'l Class: |
C09K 015/02; C01B 025/36; C01B 025/32 |
| Field of Search: |
106/462,14.12,14.13,14.14,14.21
423/629
|
References Cited
U.S. Patent Documents
| 2034519 | Mar., 1936 | Larson | 106/462.
|
| 2222199 | Nov., 1940 | Fleck | 106/462.
|
| 2974054 | Mar., 1961 | Beamesderfer | 106/482.
|
| 3342669 | Sep., 1967 | Boggess | 106/462.
|
| 4110492 | Aug., 1978 | Hayman | 106/462.
|
| 4294621 | Oct., 1981 | Maurer et al. | 106/462.
|
| 4294808 | Oct., 1981 | Wasel-Nielsen et al. | 106/462.
|
| 4773936 | Sep., 1988 | Clark et al. | 106/462.
|
| 4883533 | Nov., 1989 | Kosin et al. | 106/462.
|
| Foreign Patent Documents |
| 0035798 | Sep., 1981 | EP.
| |
| 2102542 | Aug., 1972 | DE.
| |
| 2951126 | Jun., 1981 | DE.
| |
| 0045267 | Mar., 1983 | JP.
| |
Primary Examiner: Dixon, Jr.; William R.
Assistant Examiner: Hertzog; Scott L.
Attorney, Agent or Firm: Venable, Baetjer, Howard & Civiletti
Claims
I claim:
1. Anticorrosive pigments comprising tertiary alkaline-earth aluminum
phosphates wherein the numerical atomic ratio x:y:z of the formula
AE.sub.x Al.sub.y (PO.sub.4).sub.z of alkaline earth to aluminum to
phosphate, respectively, is 40-65% to 7-25% to 25-45%.
2. Anticorrosive pigments according to claim 1, wherein the ratio x:y:z is
50-65% to 8-15% to 25-35%.
3. Anticorrosive pigments according to claim 1, comprising calcium and/or
magnesium phosphate as the alkaline-earth phosphate.
4. Anticorrosive pigments according to claim 1, wherein the numerical ratio
of alkaline-earth atoms to phosphate is 1-2.5:1 and the ratio of aluminum
proportion to alkaline-earth proportion is 0.3:1-3.5, again expressed as
numerical ratio of the atoms.
5. A process for the production of anticorrosive pigments according to
claim 1, wherein an alkaline-earth compound and aluminum compound
sufficiently soluble for reaction with phosphoric acid are reacted with
phosphoric acid and the resulting pigment is filtered off, dried and
optionally ground.
6. The process according to claim 5, wherein alkaline-earth hydroxide or
carbonate and aluminum hydroxide as well as conventional industrial
phosphoric acid are used as the starting materials
7. The process according to claim 5, wherein the pigment is dried at a
temperature above 100.degree. C., and optionally calcined at a temperature
of about 150.degree. C. or above.
8. The process according to claim 6, wherein the pigment is dried at a
temperature above 100.degree. C., and optionally calcined at a temperature
of about 150.degree. C. or above.
9. The process of claim 7 wherein the pigment is dried at about 105.degree.
C.
10. The process of claim 8 wherein the pigment is dried at about
105.degree. C.
11. Anticorrosive pigments according to claim 2, comprising calcium and/or
magnesium phosphate as the alkaline-earth phosphate.
12. Anticorrosive pigments according to claim 2, wherein the numerical
ratio of alkaline-earth atoms to phosphate is 1-2.5:1 and the ratio of
aluminum proportion to alkaline-earth proportion is 0.3:1-3.5, again
expressed as numerical ratio of the atoms.
13. A process for the production of anticorrosive pigments according to
claim 2, wherein an alkaline-earth compound and aluminum compound
sufficiently soluble for reaction with phosphoric acid are reacted with
phosphoric acid and the resulting pigment is filtered off, dried and
optionally ground as usual.
14. A process for the production of anticorrosive pigments according to
claim 12, wherein an alkaline-earth compound and aluminum compound
sufficiently soluble for reaction with phosphoric acid are reacted with
phosphoric acid and the resulting pigment is filtered off, dried and
optionally ground as usual.
15. The process according to claim 13, wherein alkaline-earth hydroxide or
carbonate and aluminum hydroxide as well as conventional industrial
phosphoric acid are used as the starting materials.
16. The process according to claim 14, wherein alkaline-earth hydroxide or
carbonate and aluminum hydroxide as well as conventional industrial
phosphoric acid are used as the starting materials.
17. The process according to claim 13, wherein the pigment is dried at a
temperature above 100.degree. C., and optionally clacined at a temperature
of about 150.degree. C. or above.
18. The process according to claim 14, wherein the pigment is dried at a
temperature above 100.degree. C., and optionally calcined at a temperature
of about 150.degree. C. or above.
19. The process of claim 17 wherein the pigment is dried at about
105.degree. C.
20. The process of claim 18 wherein the pigment is dried at about
105.degree. C.
Description
Anticorrosive pigments containing phosphate, particularly zinc phosphate,
are nowadays used as pigments for anticorrosive coatings, since they have
good corrosion-inhibiting properties.
The law on environmental protection restricts the use of pigments
containing heavy metals insofar as heavy metal contents may not exceed
certain limits in the waste to be disposed and waste water produced by the
production plants of paint manufacturers or in the water resulting from
processing (spray booths). Corresponding technical steps involving costs
have to be taken in order to prevent zinc from getting into the waste
water, for example. Although the aluminum-zinc phosphate hydrates and/or
the basic aluminum-zinc phosphate hydrates according to European patent 0
054 267, show a reduced solubility of zinc, it is still difficult to
observe the stipulated limits.
In addition to the phosphates on the basis of heavy metals, patent
literature describes secondary phosphates of the alkaline-earth metals as
anticorrosive pigments. However, their efficiency cannot be compared with
zinc phosphate. For example, calcium or magnesium hydrogenphosphates are
improved, according to European patent 0 028 290, by admixing zinc oxide,
while the anticorrosive pigments which are known from DE-PS 37 31 737 and
based upon alkaline-earth hydrogenphosphates having a content of
alkaline-earth carbonates, primarily protect against filiform corrosion on
aluminum.
The object of the present invention is to develop heavy metal-free
phosphate pigments on the basis of alkaline-earth metals, which can be
used for anticorrosive coatings in general, i.e. also for steel, and are
more efficient than the known zinc phosphates. When examining the
corrosion protection of phosphate piqments contained in a primer coating
common in practice, it was found that, in combination with aluminum,
phosphates on the basis of magnesium and/or calcium have better
anticorrosive properties than secondary phosphates, on the basis of
calcium or magnesium, and tertiary phosphates, on the basis of magnesium,
calcium and zinc.
Accordingly, the problem is solved by anticorrosive pigments on the basis
of tertiary alkaline-earth aluminum phosphates, with only magnesium and
calcium, of course, coming into consideration as alkaline earths for
practical reasons.
These anticorrosive pigments are produced in the known per see manner from
alkaline-earth and aluminum compounds sufficiently soluble in phosphoric
acid as well as phosphoric acid, e.g. alkaline-earth hydrogen or
carbonate, aluminum hydroxide and phosphoric acid, at a preferably
slightly elevated temperature, a mixed crystal forming from aluminum
phosphate and alkaline-earth phosphate. As regards the alkaline-earth
phosphate, Ca.sub.3 (PO.sub.4).sub.2.n H.sub.2 O and/or Ca.sub.5
(PO.sub.4).sub.3 OH (hydroxylapative) could be proved for calcium by means
of X-ray affraction. When the aluminum and/or alkaline-earth contents are
increased, aluminum oxide hydrate and/or alkaline-earth hydroxide may also
be present. The resulting pigments are filtered off, dried as usual and
preferably also ground depending on the intended use. Drying is carried
out preferably at 100.degree.-110.degree. C., e.g. at about 105.degree. C.
If desired, calcining may also be carried out, a temperature of at least
about 150.degree. C. usually being sufficient. However, a calcination
temperature of about 600.degree. C. or above may also be applied.
As mentioned earlier, only magnesium and calcium come into consideration
for practical reasons. For the sake of simplicity, the expression alkaline
earths (AE) is used hereinafter, even though only these two alkaline
earths are of interest.
The pigments may be represented by the formula AE.sub.x Al.sub.y
(PO.sub.4).sub.z. Hereinafter, the ratio x:y:z is referred to as the
atomic ratio or numerical atomic ratio which may also be expressed by the
formula AE.sub.x Al.sub.y P.sub.z. It is repeated expressly that this does
not include the atomic weights but, as common in the chemical spelling of
formulae, only the number of atoms or atom groups (such as PO.sub.4,
which, of course, can also be represented only by P as well). The
composition may then be given in percent by the percentage of the
individual components with respect to the total number of all components.
The mixed crystal Ca.sub.3 (PO.sub.4).sub.2.AlPO.sub.4 =Ca.sub.3
Al(PO.sub.4).sub.3 is mentioned by way of example. It has an atomic ratio
or atom group ratio of 3 Ca to 1 Al to 3 P or PO.sub.4. In this case, the
percentage of the individual components is 43% of Ca, 14% of Al and 43% of
P or PO.sub.4 .
In the inventive anticorrosive on the basis of tertiary alkaline-earth
aluminum phosphates, the ratio of the three components alkaline earth to
aluminum to phosphorus, expressed in the above-defined atomic ratio of
x:y:z, is generally 40-70% % of alkaline earth to 5-30% of aluminum to
20-50 % of phosphorus or phosphate, the amounts, of course, being chosen
such that 100% result each time. This ratio is preferably 40-65% of
alkaline earth to 7-25% of aluminum to 25-45% of phosphorus, and a ratio
of 50-65% of alkaline earth to 8-15% of aluminum to 25-35% of phosphorus
is particularly preferred.
Thus, it is apparent that relatively more alkaline earth than aluminum and
phosphorus is present in the particularly preferred range. The
anticorrosive effect is improved when the amount of magnesium and calcium
is relatively higher than that of aluminum and phosphorus, but, also
within the general ratio, it is markedly above the anticorrosive effect of
e.g. zinc phosphate.
The following examples explain the invention and show the results of the
anticorrosive test.
EXAMPLE 1
A magnesium-aluminum phosphate hydrate forms when reacting magnesium oxide
and/or magnesium carbonate as well as aluminum hydroxide in 10-40% aqueous
suspension with conventional industrial phosphoric acid (about 75% by
weight).
1 mole of magnesium oxide and 0.2 mole of aluminum hydroxide are used
together with 0.6 mole of commercial industrial phosphoric acid (about 75%
by weight). The reaction results in slight heating so that, starting from
room temperature, a reaction temperature from 30.degree. to 60.degree. C.
adjusts depending on the amount of batch. A magnesium aluminum phosphate
hydrate forms, whose atomic ratio of magnesium to aluminum to phosphorus
is 1.66:0.33:1, i.e. 56% 11% 33% when expressed in percent. The pigment
obtained in the reaction batch is filtered off as usual, dried and,
depending on intended use, optionally ground. Each of the batches
according to the examples was dried at 105.degree. C. Calcining may
optionally be carried out as well.
EXAMPLE 2
A calcium-aluminum phosphate hydrate forms when reacting calcium hydroxide
and aluminum hydroxide in 10-40% aqueous suspension with conventional
industrial concentrated phosphoric acid (75% by weight).
1 mole of calcium hydroxide and 0.16 mole of aluminum hydroxide are reacted
with 0.5 mole of phosphoric acid (75 %) at temperatures from 30.degree. to
60.degree. C. Aluminum phosphate forms a mixed crystal together with
calcium phosphate which, when investigated by means of X-ray diffraction,
consists of Ca.sub.3 (PO.sub.4).sub.2.n H.sub.2 O, data card No. 18-303,
edition 1986, or Ca.sub.5 (PO.sub.4).sub.3 OH (hydroxylapatite, data card
No. 0-436, edition 1986). The atomic ratio of calcium to aluminum to
phosphorus is 2:0.3:1. The precipitated pigment is further treated as
indicated in Example 1.
A mixture of alkaline earths may also be present in the alkaline-earth
aluminum phosphates using a mixture of the alkaline-earth compounds.
Correspondingly, instead of adding the phosphoric acid to the suspension of
the alkaline-earth hydroxide or carbonate and the aluminum hydroxide, the
aluminum hydroxide, for example, may be dissolVed in the phosphoric acid,
and then this component may be added to the suspension of the
alkaline-earth compound or, vice versa, the suspension of the
alkaline-earth compound may be added to the reaction mixture consisting of
aluminum hydroxide and phosphoric acid. For this purpose, the phosphoric
acid used is usually the common industrial type having about 75% by
weight, since it is the most inexpensive and meets the requirements for
purity stipulated herein.
In addition to the pigments used in Examples 1 and 2, which are referred to
as pigments 2 and 5 in Table 1 below, the other pigments of this Table
were also obtained as according to Examples 1 and 2.
The investigation and evaluation of the anticorrosive behavior of these
pigments were carried out as follows:
The anticorrosive pigments of the following Table 1 were investigated in a
primer coating in the salt spray test and humidity test with respect to
their anticorrosive effect in comparison with tertiary magnesium, calcium
and zinc phosphate as well as a secondary calcium phosphate.
______________________________________
Binding agent short-oil alkyd resin
PVC/CPVC (pigment volume
concentration/critical
pigment volume concentration
0.7
formulation example
see Table 2
dry film thickness
45 +/- 5 microns
drying conditions
7 days at room temperature
and 2 hours at 50.degree. C.
anticorrosive test
Salt spray test, ASTM D714-56
after 360 hours
Humidity test, ASTM D2247-68
after 500 hours
evaluation 30 minutes after weathering.
______________________________________
In order to evaluate the anticorrosive behavior, data conforming to the
standards, such as degree of blistering according to ASTM D 714-56,
creepage at the scribe according to ASTM D 1654-75 and corrosion of the
metal surface according to ASTM D 610-68, is rated according to the
enclosed evaluation pattern of Tables 3 and 4 and combined to an overall
evaluation (rating) (100=best anticorrosive value, 0=poorest anticorrosive
value).
In order to accurately determine the degree of rusting, the coatings were
removed by pickling from the base material by means of methylene chloride
after weathering.
TABLE 1
__________________________________________________________________________
Anticorrosive test - results of short-term weathering
Overall rating
Salt spray test ASTM D 714-56 after
360 hours Humidity test ASTM D 2247-68
Creepage at
Degree of
after 500 hours
Degree of
the scribe
rating Degree of
atomic
blistering
ASTM ASTM Degree of
rusting
ratio
ASTM D 1654-74
D 610-68
rat-
blistering
ASTM D
rat-68
x:y:z
D 714-56
(in mm)
(in %)
ings
ASTM D 714-56
(in %) ings
__________________________________________________________________________
Zn.sub.3 (PO.sub.4).sub.2.x H.sub.2 O
80
(8F)
65 (2) 20 (33)
46 50 (6M) 0 (50) 17
Mg.sub.3 (PO.sub.4).sub.2.x H.sub.2 O
80
(8F)
70 (1,5)
20 (33)
48 65 (4F) 0 (50) 22
CaHPO.sub.4 .x H.sub.2 O
65
(4F)
35 (8) 20 (33)
35 45 (0) 0 (50) 15
Ca.sub.5 (PO.sub.4).sub.3 OH
65
(4F)
80 (1) 20 (33)
46 45 (4M) 0 (50) 15
Pig. 1
Mg.sub.x Al.sub.y (PO.sub.4).sub.z.n H.sub.2 O
1:0,3:1
70
(<4F)
80 (1) 20 (33)
48 55 (8M) 20 (33) 31
Pig. 2
" 1,66:0,3:1
70
(<4F)
70 (1.5)
60 (10)
65 55 (8M) 40 (16) 45
Pig. 3
Ca.sub.x Al.sub.y (PO.sub.4).sub.z.n H.sub.2 O
1:0,3:1
60
(2-4F)
65 (2) 20 (33)
41 70 (6F) 0 (50) 23
Pig. 4
" 1,7:0,3:1
70
(6F)
65 (2) 70 (3)
69 55 (8M) 60 (10) 58
Pig. 5
" 2:0,3:1
60
(2-4F)
70 (1,5)
40 (16)
53 30 (6MD)
60 (10) 50
Pig. 6
" 2,5:0,3:1
65
(4F)
35 (8) 20 (33)
35 65 (4F) 0 (50) 22
Pig. 7
" 2:0,4:1
60
(2-4F)
80 (1) 70 (3)
70 35 (8MD)
60 (10) 52
Pig. 8
" 2:0,8:1
70
(<4F)
80 (1) 60 (10)
68 55 (8M) 40 (16) 45
__________________________________________________________________________
When investigating corrosion protection by means of the salt spray test,
anticorrosive properties were obtained by the new anticorrosive pigments,
which were better than those of secondary calcium phosphate and tertiary
magnesium, calcium and zinc phosphate. Particularly, the degree of rusting
was markedly reduced on the metal surface.
As shown in the above Table 1 containing the results of short-term
weathering, the humidity test also revealed that the degree of rusting is
reduced by the new pigments.
Below, Table 2 shows the formulation for the production of a primer coating
by means of pigment 4 serving as an example; Tables 3 and 4 give the
rating pattern for the results of Table 1.
TABLE 2
______________________________________
Formulation: parts by weight %
______________________________________
short-oil alkyd resin, 60%
46.8
(34% of special fatty acids)
modified montmorillonite as an
0.4
anti-settling agent
glycol ether 1.7
xylene 11.3 premix bin-
ders, solvents
and additives
calcium octoate 10% Ca
0.1
pigment 4 5.4
natural barium sulphate
17.4 disperse in
a pearl mill
magnesium silicate 9.8
titanium dioxide rutile
5.6
lead-free siccative 1.2 stir in sep-
arately one af-
ter the other
antioxidants 0.3
100.0
______________________________________
PVC in % = 31
PVC/CPVC = 0.7
non-volatile content in %
= 67
______________________________________
TABLE 3
______________________________________
TABLE OF EVALUATION
Creepage at the
Degree of blister-
scribe given in mm
Rating ing ASTM D 714-56
ASTM D 1654-74
______________________________________
100-90 -- 0-0.4
90-60 8 F-2 F 0.8-3.2
55-40 8 M-2 M 4.8-6.4
35-20 8 MD-2 MD 9.5-12.7
15-0 8 D-2 D 15.9-25
______________________________________
TABLE 4
______________________________________
degree of rusting
rating ASTM D 610-68
______________________________________
100 very good no corrosion or less than 0.01%
80 good spot-like corrosion, but less
than 1-3%
60 good - moderate
10% of the surface corroded
40 moderate 16% of the surface corroded
20 poor 33% of the surface corroded
0 very poor 50% of the surface corroded
______________________________________
Overall Rating
To obtain the overall rating according to salt spray and humidity test
weathering, the individual ratings are added and divided by 4 and 3,
respectivley, the ratings mentioned in TABLE 4 being counted twice because
of their greater importance.
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